@article {Ospelkaus2010, title = {Quantum-state controlled chemical reactions of ultracold potassium-rubidium molecules}, journal = {Science}, volume = {327}, number = {5967}, year = {2010}, month = {feb}, pages = {853{\textendash}7}, abstract = {How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single partial-wave scattering, and quantum threshold laws provide a clear understanding of the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near-quantum-degenerate gas of polar 40K87Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules were prepared in a single quantum state at a temperature of a few hundred nanokelvin, we observed p-wave-dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a short-range chemical reaction with a probability near unity. When these molecules were prepared in two different internal states or when molecules and atoms were brought together, the reaction rates were enhanced by a factor of 10 to 100 as a result of s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.}, keywords = {2010}, issn = {1095-9203}, url = {http://www.sciencemag.org/content/327/5967/853.abstract}, author = {Ospelkaus, S. and Ni, K.-K. and Wang, D. and de Miranda, M. H. G. and B Neyenhuis and Qu{\'e}m{\'e}ner, G and Paul S Julienne and Bohn, J L and D S Jin and Jun Ye} }